I was wondering if I replaced my big honkin gear driven alternator with a belt driven one would I possibly increase my fuel mileage?I 've been told the gear driven ones take 30 to 40 horse power to turn when charging.

Also I want to put a 12 volt alternator on my bus to keep house batteries charged. Whats the best and least expencive route to go for that one?I have removed my commpressor for my air conditioning so I can have a place to put the two alternators.For those of you not familliar with my bus it is MCI 8 with 8v92 DDEC and Allison 740A ATEC. I am currently getting 5.8 MPG and am desperate to increase it.

Seriously, I think you're looking to save pennies here. The power coming out of the alternator has to come from someplace. Don't matter whether you use a tiny 50 amp alternator or that big DN50. It'll take the same amount of power to charge the batteries and once they're full, it don't take any more power to drive the unloaded alternator. So going to a smaller alternator will only take longer to charge, but it'll still take the same amount of power, and therefore, fuel.

My opinion only.

By the way, didn't you present some other odd ideas recently about increasing fuel mileage? Something to do with tag axles? Where'd that end up?

Since I actualy drive my bus Any little amount of fuel mileage increase would be of help. lets say if not using the tag saved me a1/2 mile mpg and the alternator did the same that would be a significant savings. I didn't say it was a smaller alternator just belt driven. I have it from the old bus and it was a reman. unit from detroit city busses. I don't really think any Idea is crazy if it saves me fuel. Just asking before I do it so I don't do any thing crazy. No need to beat me up for trying to better my fuel consumption.

I don't think you would see any difference between the two drive methods for an alternator. If they are both putting out the same amount of energy then they are both going to require the same amount of energy into the alternator.

Now you want a 12 volt alternator for house batteries. If you leave the gear drive in place for the main batteries, that would allow you to use the belt grooves that were for the air conditioning to drive a 12 volt alternator. Now you don't have to come up with brackets for a new 24 volt alternator and all the design headaches that would entail. The only brackets that you need to come up with are the brackets for the 12 volt alternator.

The efficiency of energy transmission through a gear train is very high - in theory not far off 100%, although in practice you have losses through friction between shafts and bearings etc. A chain is less efficient, and a belt less efficient still, due to the energy required to 'bend' the belt material. But, as has been said, the actual differences will be negligible. As has also been said, to get a certain amount of power out of an alternator you need to put a certain amount of power into it, so again in theory it doesn't matter how big the alternator is. More modern alternators are probably slightly more efficient due to advances in design and technology, but I doubt whether the saving would be worth the purchase cost.

I don't see any reason why you couldn't temporarily disconnect your existing big alternator and record your fuel economy on a trip to see what difference it makes. If you do it during the daytime and avoid any unnecessary electrical use you will be able to go much further than you expect without battery charging.

Regarding the house batteries - have you considered either a dual output alternator regulator, or a battery-to-battery charger? Both options would avoid the need to fit a second alternator.

Ron, the amount of energy need to propel the bus down the highway at a given speed is pretty much standard on unmodified buses. The things we can do are one, decrease the "load", which is what you and some of the rest of us are looking at and two, increase the efficiency of conversion of diesel fuel to energy.

Under item one, you can do things like make the bus more aerodynamic (a plane fuselage would be far more efficient that a flat nose bus, but who would want that?). You can drive without power steering or air conditioning. You can change the auto tranny to a manual with overdrive. I am looking at installing an air clutch on the fan drive to unload the fans when not needed. Each one of these options involves weighing the cost of the modifications and the inconvenience against the gain.

One thing I learned during my truck driving days was the use of synthetic oil. If you replace all the fluids EXCEPT THE ENGINE OIL with synthetics, you will decrease the amount of energy needed to move the bus. I picked up almost 2 MPG when I changed my '74 Diamond Reo to synthetics. Granted, I was carrying more weight and had two differentials, but there will still be a difference. There is some disagreement as to wether synthetics meet DD’s engine specs. I used them in mine but they will find EVERY leak no matter how small. There is another thread on the board about wheel bearings. I started out with grease in all bearings but changed to oil bath after the axle and seal manufacturers produced parts to do it. I could then use synthetic oil in all bearings.

I am assuming you always keep the tires at the correct pressure and your speed is reasonable. My experience with cruise control was that it did not do as well MPG wise as I could. I think the reason is cruise cannot anticipate hills and I can.

Under item two, you can increase the efficiently of the engine (the part that converts fuel to energy to mechanical motion). This is usually done by turbo charging, after cooling, computer controls, and such like. Again, you will have to do a cost/benefit analysis.

Keep trying! All of us will benefit. I think Thomas Edison said after his 100th failure at inventing the electric light, “ I have not failed, I just know 100 ways it will not work”.

Legal disclaimer: This is my opinion. It and one dollar will buy you a cup of coffee in some places.

I was wondering if I replaced my big honkin gear driven alternator with a belt driven one would I possibly increase my fuel mileage?I 've been told the gear driven ones take 30 to 40 horse power to turn when charging.

Also I want to put a 12 volt alternator on my bus to keep house batteries charged. Whats the best and least expencive route to go for that one?I have removed my commpressor for my air conditioning so I can have a place to put the two alternators.For those of you not familliar with my bus it is MCI 8 with 8v92 DDEC and Allison 740A ATEC. I am currently getting 5.8 MPG and am desperate to increase it.

Captain Ron

You wouldn't save anything on mileage by changing the alternator. Your particular engine/transmission combination is part of the problem, since the 740 doesn't have overdrive the engine is turning pretty fast at highway speeds. Save the money and aggravation and look for a usable overdrive transmission like a World or B500 and get the rpms down which will use less fuel.

My 6V92TA with the 740 gets 6 mpg and I have no horsepower to spare, Yours is a beast and can generate a lot of horsepower which costs in fuel usage. Even if you drive it with a feather-foot it won't get better like it sounds like you expect. It's just not possiblewith the combination that you have. You may be able to get Detroit to turn down the power levels and torque curve but that probably wouldn't help all that much.

Maybe a repower to a series 50 or cummins might help but you would still need an overdrive tranny to do proper respect to the amount of economy that you want. But think about this, That $20,000 for a repower will buy lots of fuel and regular maintenance on that 8V92 for a long time.

The next question would be whether the coach is worth the additional investment. You might just start shopping again to get something more modern with a modern 4-stroke package in it.

When my MC9 dies it goes to the scrap-yard directly after removal of the good stuff. Not worth the aggravation of repowering with the prices falling now on the more modern stuff.

Since I actualy drive my bus Any little amount of fuel mileage increase would be of help. lets say if not using the tag saved me a1/2 mile mpg and the alternator did the same that would be a significant savings. I didn't say it was a smaller alternator just belt driven. I have it from the old bus and it was a reman. unit from detroit city busses. I don't really think any Idea is crazy if it saves me fuel. Just asking before I do it so I don't do any thing crazy. No need to beat me up for trying to better my fuel consumption.

Capt Ron,

Sorry if my tone seemed offensive. Wasn't my intent to beat you up. I just found it curioius that you are coming up with some "different" ideas to try to save fuel. Certainly not bad. Just interesting that you are "thinking out of the box", so to speak.

I really don't think you'll see a savings changing out the alternator, but I may be wrong. Haven't read the rest of the replies yet. I'm sure there are those who will disagree with me.

I know you use your bus to get to various gigs. Just out of curiosity, how many miles do you put on the bus in a year's time?

My cruise is not working at this time but when it did I tried setting it at 60 MPH and 55 MPH and got no better results. So it's time for other options.

You can't run a couple hundred miles at a slightly lower speed and then say you didn't save anything. I've kept track of every litre of fuel that went into our bus since we bought it three years ago. Over 40,000 km we averaged 6.2 miles to the Canadian gallon, all in - generator, Pro Heat, towing, empty. That mileage was running with the big dogs. If the speed limit was 75 I ran 8 over. I have no idea what our average speed was but we never ran slow. In the third year I ran a couple of significant trips (3 or 4000 km per trip) at a maximum of 90 km (roughly 55 MPH). That got me 9 MPG. I don't plan to run 55 all the time but now I know exactly what it costs me when I don't.

There is no doubt that slowing down will save you fuel. And it will save you more fuel more easily than any other alternative or combination of alternatives. It only stands to reason - you burn up fuel to do work. It takes more work to get there faster. Its no more complicated than that.

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R.J.(Bob) EvansUsed to be 1981 Prevost 8-92, 10 spdCurrently busless (and not looking)My websiteOur weblogSimply growing older is not the same as living.

I've noticed similar results on my trips. if I'm trying to run 70+, I get 5.5 to 6. If I'm relaxing and doing around 60-65, I get 6.5 to 7. Doesn't seem to matter if I'm climbing hills or running flat interstate at 60, I still get about the same 6.5 to 7. Won't be getting anywhere near 9 cause like Sammy says, "I can't drive..... 55!!!!"

On the 8V-92TA DDEC, the ideal rpm to cruise at is 1,600rpm, with as high as 1,800rpm alright. To cruise at 65mph at 1,600rpm, you would need (I assume you run 12R-22.5 tires?) a 3.08 ratio. With a starting gear of 3.692 and figuring 2.0 converter ratio and a heavy weight of 50,000lb, that works out to be a startability of 28% (anything over 20% is fine). Also, in trucking the rule of thumb is for every mile per hour over 55mph, you loose .1 mpg up to 65mph. Over 65mph you loose .15mpg for every mph up to 75mph. So going from a base line of 55mph to 75mph, your mileage will be 2.5mpg less. If you are going to keep the bus for awhile, regearing is a good way to go. With DDEC, you could change to the World B500 with it set for a 5 spd (the 6th probably would be to much of an overdrive). Either regearing or changing to the World transmission will cost $2-5000.00 minimum. I was going to change my V730 from the 4.625 to 4.11 until I found out it would be around $2,000.00. Also, I only have 3 speeds to play with and a 65mph cruise at 2100rpm is just fine (8V-71T w/ air to air intercooling). Another fuel savings would be to remove the aftercooler in the valley of the block under the blower and change to the air to air intercooling. Could mount it on the right side where the A/C was powered by electric fans. Good Luck, TomC